THE NPO FATIGUE TESTER - Niagara Foot Tester.pdf · The NPO Fatigue Tester Ziolo, Zdero, and Bryant (2001) 2. WORK TO DATE SUMMARY The Niagara FootTM was designed by the Human Mobility

THE NPO FATIGUE TESTER: THE DESIGN & DEVELOPMENT OF A

NEW DEVICE FOR TESTING PROSTHETIC FEET

Tara Ziolo, B.Sc.E

Rad Zdero, Ph.D

Tim Bryant, Ph.D, P.Eng

THE NPO FATIGUE TESTERTM: THE DESIGN AND DEVELOPMENT OF

A NEW DEVICE FOR TESTING PROSTHETIC FEET

Tara Ziolo, B.Sc.E

Radovan Zdero, Ph.D

J. Timothy Bryant, Ph.D, P.Eng

Human Mobility Research Centre (HMRC) Apps Medical Research Centre, Angada 1

Kingston General Hospital, Kingston, ON, Canada and

Mechanical Engineering Department Queen’s University, Kingston, ON, Canada

(i)

The NPO Fatigue TesterTM Ziolo, Zdero, and Bryant (2001)

EXECUTIVE SUMMARY

The ongoing problem of amputations resulting from land mines in developing and post-

conflict countries such as El Salvador, Nicaragua, Cambodia, Croatia, and Angola provides

the impetus for the current study. Although the need for community based rehabilitation in

these areas is recognized as advantageous, it is carried out often without the use of

appropriate context-sensitive prosthetic technology.

To this end, the overall purpose of the present ongoing investigation is the development

of a lower limb prosthetic system - starting with the foot - that is affordable for the target

population, highly functional, esthetically and culturally acceptable to users, and

scientifically validated through a series of clinical, field, and laboratory studies.

Briefly, this document outlines the scientific work done to date in the development of the

Niagara Foot, provides a literature survey of previous mechanical cyclic fatigue testers for

assessing prosthetic feet, describes the design and development of the current NPO Fatigue

Tester, discusses the preliminary test results for Niagara and SACH feet using the this tester,

and gives consideration to future work.

This work is being done by the Human Mobility Research Centre (Kingston General

Hospital and Queen’s University, Kingston, ON) in conjunction with Niagara Prosthetics and

Orthotics (St. Catherines, ON).

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TABLE OF CONTENTS

(iii)

EXECUTIVE SUMMARY (ii) 1 BACKGROUND 1 1.1 The Need 1 1.2 The Rehabilitation Goal 1 1.3 The Technical Goal 1 2 WORK TO DATE SUMMARY 2 2.1 Niagara Foot Shape 2 2.2 Material Selection 2 2.3 Stress Analysis 2 2.4 Action Tests 2 2.5 Clinical Trials 5 2.6 Final Design Optimization 5 3 REVIEW OF FATIGUE TESTER LITERATURE 6 4 DESIGN OF THE NPO FATIGUE TESTER 11 4.1 Mechanical Components 11 4.2 Pneumatics 15 4.3 Electrical/Control System 15 4.4 Electrical/Computer System 19 5 OPERATING PROCEDURES FOR THE NPO FATIGUE TESTER 20 5.1 Preparation of the Prosthesis for Testing 20 5.2 Test Startup Procedure 20 5.3 Test Conditions 22 6 A PILOT STUDY USING THE NPO FATIGUE TESTER 23 6.1 Materials and Methods 23 6.2 Results and Discussion 23 7 INITIAL MATERIALS TEST RESULTS 25 7.1 Summary 25 7.2 Proof Testing 25 7.3 Cyclic Testing 26 8 FUTURE WORK 28 8.1 Validation and Calibration of the NPO Fatigue Tester 28 8.2 Waveform Modifications 30 8.3 Environmental Durability of the Niagara Foot 30 8.4 Complete Sized Modular System 31 8.5 Cosmetic Cover for Foot 32 8.6 Modification of Test Stands 32 9 FINAL REMARKS 33 REFERENCES 34

APPENDIX 1 – ISO Testing Standards for Prostheses

APPENDIX 2 – U.S. Patent for the Niagara Foot APPENDIX 3 – Material Properties APPENDIX 4 – PPC Calibration Tables APPENDIX 5 – Control System (Technical Report)


APPENDIX 6 – Test Stand Modifications APPENDIX 7 – Results of Proof Testing APPENDIX 8 – Inspection Sheets for Cyclic Testing APPENDIX 9 – Cyclic Fatigue Testing Report APPENDIX 10 – Deformation of Feet During Cyclic Testing

(iii)

The NPO Fatigue Tester Ziolo, Zdero, and Bryant (2001)

1. BACKGROUND 1.1 The Need The current project’s motivation is the ongoing problem of amputations resulting from land

mines, especially in developing and post-conflict countries such as El Salvador, Nicaragua,

Cambodia, Croatia, and Angola. About 70 people per day are killed or injured due to

landmines, of which 110 million still lay active in the ground on every continent

(www.oneworld.org/guides/landmines/stats.html). The Canadian government, universities,

service organizations, and the private sector have been leaders in addressing this problem.

1.2 The Rehabilitation Goal

The uniqueness of the current project is two-fold. First, most governments have invested in

programs promoting dependence on costly solutions and centralized institutional approaches

to rehabilitation, even though the majority of landmine survivors are from rural areas. As an

alternative, the internationally recognized concept of Community Based Rehabilitation

(CBR) develops innovative programs that help disabled people rely less on centralized social

and health systems, live more independently, and be re-integrated into their communities.

This project uses CBR as its philosophy to address equipment needs for disabled people.

Second, prostheses typically provided have been inappropriate for developing and post-

conflict countries, in that they have been far too expensive for poor clients, especially since

they must be replaced frequently throughout one’s life, and were designed to fit urban

Western environmental conditions. On the other hand, the Niagara FootTM (Niagara

Prosthetics and Orthotics, St. Catherines, ON, Canada), was designed to be highly functional

in these environments, but at only 1/10TH the price of other commercial prosthetic feet.

1.3 The Technical Goal

This report describes the design and development of a mechanical cyclic fatigue tester,

namely the NPO Fatigue TesterTM, to assess prosthetic feet as a predictor of field service life.

Specifically, using ISO (International Organization for Standardization) testing standards

(Appendix 1), the Niagara FootTM is to be compared to and tested in parallel with a popular

commercially available foot, namely the SACH (Solid Ankle Cushion Heel), which is often

exported from the West to places of need.

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http://www.oneworld.org/guides/landmines/stats.html


2. WORK TO DATE SUMMARY The Niagara FootTM was designed by the Human Mobility Research Centre (HMRC, Queen's

University and Kingston General Hospital, Kingston, Canada) and the Ergonomics Research

Group (ERG, Queen's University, Kingston, Canada) under contract with Niagara Prosthetics

and Orthotics (NPO).

2.1 Niagara FootTM Shape

The first step was the design and construction of an inexpensive and high-function foot

component, a lengthy iterative process, modular with existing prosthesis shafts being used in

the host nation. The modular foot component is unique because of its single unit construction

and its ability to be mass-produced in a few standard sizes (Fig. 1).

2.2 Material Selection

The material used to manufacture the Niagara foot is another critical factor in its success.

After considering the stress analysis effects and load-deflection characteristics of a wide

variety of potential materials, a preliminary shape of the Niagara foot [Series 1] was

developed (Fig. 1a) composed of a medium modulus injection-moldable thermoplastic (Tsai,

1999). The selection was done in tandem with the stress analysis described below.

2.3 Stress Analysis

The Niagara Series 1 foot shape was assessed using computer Finite Element Analysis (FEA)

by our group for a variety of materials (Ziolo, 1999). The model predicts the mechanical

stress levels the foot would experience under extreme conditions of normal use, i.e. at heel

strike and toe off. Heel strike load (700 N) was applied at 15° whereas toe off load (700 N)

was applied at 45°. From Fig. 2, it was evident that for a given set of material properties, the

inner-C portion was the most susceptible to experiencing highest stress.

2.4 Action Tests

The FEA model was verified with a load-deflection test using an Instron tester (Tsai, 1999).

The Niagara [Series 1] foot was instrumented with IREDs (infra-red emitting diodes) and

mounted onto the Instron (Fig. 3). A 5-70 kg cyclic force was applied separately at the toe

and heel at 45° and 15°, respectively, and the resulting angular deflections videotaped and

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(b)

(a)

(c)

Fig. 1. Design Iterations of the Niagara Foot. (a) Niagara Foot [Series 1] (b) Niagara Foot [Series 2] (c) Niagara Foot [Series 3] final design shape being tested currently.

Figure 2. FEA Stress Analysis on the Niagara Foot [Series 1] prosthesis. The inner-C section experiences the highest von Mises stress levels.

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(a) (b)

Fig. 3. Load-Deflection Tests on the Niagara Foot [Series 1]. Forces were applied at (a) toe and (b) heel and the deflections were determined.

Computer

Infrared EmittingDiodes (IREDS)

(a) (b) Fig. 4. Clinical Gait Trials on the Niagara Foot [Series 1] and SACH. (a) clinical gait test setup (from Noce-Kirkwood, 1997). (b) photo of a below knee amputee subject walking with the Niagara Foot [Series 1]. Results showed that the Niagara Foot [Series 1] is a highly functional foot with positive feedback from subjects, equal to or better than the SACH.

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later analyzed. The action tests yielded a toe stiffness result of 24 kN/m compared to the FEA

model result of 14.8 kN/m.

2.5 Clinical Trials

The Niagara Series 1 and a SACH type foot were clinically tested with 4 amputees (Potter

2000; Potter et al., 1999). These quantitative tests involved videotape footage and computer

controlled gait analysis equipment (Fig. 4). Results indicated no statistical difference (p >

0.05) in the velocity (Niagara Series 1 - 67.01 m/min, SACH - 64.54 m/min) and cadence

(Niagara Series 1 - 100.38 steps/min, SACH - 101.38 steps/min) between the prostheses.

However, the Niagara Series 1 statistically outperformed (p < 0.05) the SACH with respect to

stride length (Niagara Series 1 - 1.33 m, SACH - 1.27 m) and % stance phase (Niagara Series

1 - 61.24 %, SACH - 64.95 %). Qualitative feedback from the subjects, using a standardized

questionnaire and personal interview, showed amputee satisfaction with the Niagara foot in

terms of stability, effectiveness, and comfort. Subjects indicated no significant difference

between the Niagara Series 1 and SACH.

2.6 Final Design Optimization

Because the foot stiffness target was 50 kN/m after the ISPO (1978) standard, the Niagara

Series 1 shape was further optimized to arrive at the Niagara Series 2 by Ziolo (1999) (Fig.

1b). Subsequent patient considerations and stress analysis led to further design modifications,

which concluded with the Niagara Foot [Series 3] shape currently being used (Fig. 1c), full

technical for which can be found in Appendix 2. The final material chosen was the acetal

resin Delrin 150E, the material and mechanical properties for which can be found in

Appendix 3.

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3. REVIEW OF FATIGUE TESTER LITERATURE In addition to the numerous clinical gait studies of prosthetic lower limbs and feet have been

conducted (Barth et al., 1991; Macfarlane et al., 1990; Menard and Murray, 1989; Pitkin,

1995; Potter et al., 1999; Valenti, 1990; Yamamoto et al., 1992), a survey of the literature has

revealed several studies involving mechanical fatigue testing of prosthetic feet or other

orthotic devices.

The earliest fatigue tester the current authors are aware of was developed by Daher

(1975). It consisted of a Scotch-Yoke mechanism simulating the kinematics of the knee and

foot, providing both the swing and stance phases of gait (Fig. 5). The tester had a mobile flat

ground plate with which foot contact was made as the mechanism cycled through, with heel-

strike and toe-off occurring at 20° and 35°, respectively. Load levels were controlled by

timed cams that cyclically pressurized the air contained in pneumatic cylinders. Stance load

levels were maintained at a relatively constant level until just prior to toe-off. Daher’s study

involved evaluating 9 types of SACH feet, applying socks and shoes to two simultaneously

tested prosthetic feet, which were initially aligned at 5° toe-out. The feet were cycled up to

500,000 cycles and maximum loads of 100 kg (981 N), with several load-vs-deflection

checks during the entire test regimen. Most of the permanent deformation, due to compacting

and breakdown of foam, occurred within the first 5000 cycles as evidenced from X-rays of

the feet and hysteresis in the load-deflection curves. The major advantages of this system

were that it was force controlled in order to reproduce general loading pattern and had the

capability of testing two feet simultaneously. However, the axial load levels were far below

the peak levels normally experienced by prosthetic feet during in-service use (approx. 1350

N) for a 150 lb person, thereby artificially extending the longevity of the prostheses tested.

A displacement control device previously developed by our group consisted of a cam-

driven rocker ground plate that created 17-20° and 57-61° angles, respectively, with

prosthetic test feet at heel-strike (HS) and toe-off (TO) positions, as shown in Fig. 6

(Singleton, 1983; Wevers and Durance, 1987). The tester was capable of durability testing of

an entire foot-shank-socket complex. The ground plate had adjustable inversion/eversion

settings in order to test the effect of improper prosthetic fitting or use when desired; the effect

of this would normally be felt at the socket or contralateral hip. It was driven by a 110 V

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Heel Strike Toe OffRotating Pin

Fixed Pin

Mobile Ground Plate

Disk Disk

GroundPlate

A B

Fig. 5. Fatigue Tester as proposed by Daher (1975) (A) schematic (B) photo of tester.

b

c

c

a

d

e f

g

Fig. 6. Fatigue Tester designed and constructed by Singleton (1983) and Wevers and Durance (1987): [a] - shaper crank, [b] - cam, [c] - sliders, [d] - connecting rod, [e] - upper crank, [f] - rocker plate, [g] - spring loaded stop.

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synchronous electric motor through a reduction gear box, with displacement control cams

ensuring proper kinematics during 1 Hz cycling was simulated. Due to softening of prosthetic

feet during repetitive motion and in order to meet the ISPO standard 1350 N maximum axial

load, a force sensor was mounted on the shank support bar to provided force feedback. In

between TO and HS, no load was applied to simulate the swing phase. This 0-1350 N loading

pattern was cycled a minimum of 3 million times or until prosthesis failure, evidenced by

either sudden catastrophic failure of the metal Otto Bock foot-shank connector, the

appearance of cracks in the plastic socket, or cracking in the soles of the feet. In their study,

Wevers and Durance (1987) tested 4 different SACH feet and found that they showed cracks

in the soles at between 43,800 and 105,000, reaching only 1.5-3.5 % of the 3 million cycles

required by ISPO and ISO standards. Plastic residual limb sockets tested separately,

however, reached an average of 415,000 cycles before failure. The appeal of this tester is that

it both simulated the load transfer from heel to toe and provided material recovery during

swing phase, mimicking actual use more closely and was able to test durability of an entire

foot-shank-socket complex. However, because loading patterns and levels were dependent on

accurate cam design, the authors recommended future modifications to include the use of

hydraulic semi-controlled machine.

Carlson et al. (1990) developed a durability tester designed to test ankle-foot orthoses

(AFOs), specifically those constructed from polyurethane and polypropylene. It consisted of

a central mounting shaft onto which four AFOs were attached at the foot segment and

weighted at the shank end (Fig. 7). As the entire system cycled at 14 cycles/min (0.23 Hz),

the AFOs were rotated backwards causing maximum dorsiflexion of up to 250°. As the

AFOs were rotated over the top of the cycle, the weighted shank would suddenly fall,

‘banging’ the orthosis against its plantarflexion stop. The inertia of the shank weights (1 and

1.95 kg-m) was such that they created significant sheer, torsion, and tension ‘shock’

transmitted to the attachment interface during the sudden ‘bang’. The failure criterion was the

creation of fatigue cracks at the flexural interface. Although the apparatus did not yield

results capable of predicting AFO service life, it was a good relative measure in comparing

durability of AFOs of varying designs and material compositions.

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Fig. 7. Cyclic Fatigue Tester for ankle-foot orthoses (AFOs) developed by Carlson et al. (1990).

E

Fig. 8. Simplified Fatigue Tester proposed by Toh et al. (1993): A - plate, B - angle block, C - cam, D - load cell, E - variable speed induction motor.

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A more recent approach by Toh et al. (1993) has been to avoid simulating the complex

loading patterns experienced during normal walking and move to a simpler apparatus in

which the toe and heel are tested separately up to an appropriate peak axial load level (Fig.

8). The toe and heel were tested with sinusoidal cyclic axial loads peaking at 1.5 x body

weight (approx. 600 N) at 2 Hz up to 500 000 cycles. Blocks wedges of 30° and 15° were

used to create inclines for testing the prosthesis forefoot and heel, respectively. Static load

deflection tests were conducted between cyclic runs to detect mechanical property changes in

the foot. No impact loads simulating external events or protective footwear was used. Their

results for the Lambda foot and the Kingsley and Proteor SACH feet were consistent with

other studies using more complex fatigue tester systems. Although the appeal of this system

lies in its simplicity and is capable of testing individual prosthetic feet, it would need to be

significantly modified to mimic more closely actual ground reaction loading patterns and to

test foot-shank-socket complexes.

A commercially available system, the Universal Testing Machine (UTM) from Endolite-

Blatchford (Hampshire, UK, www.endolite.com) is a structural testing device capable of

testing one or two prosthetic feet simultaneously. Typical technical specifications include: 1

Hz cycling frequency, 5000 N maximum axial force, 60 mm stroke length at toe off, 30 mm

stroke length at heel strike, 400-500 kg weight, 1.3x1.6 m size, and 110/240 VAC and 4 amp

power requirements. The tester is available at a cost of $ 7000 U.S. (£ 3500), is computer

controlled with pneumatic actuators requiring 325-650 L/min of air, and capable of up to

5000 N of axial load. Although available commercially, the manufacturer’s product

catalogue does not disclose criteria used to indicate prosthesis failure, calibration procedures,

or hysteresis effects. The current authors are unaware of any validation tests or applications

of this unit described in the scientific literature.

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http://www.endolite.com/


4. DESIGN OF THE NPO FATIGUE TESTERTM The following description of the current tester is that of a working model which will include

several design modifications, as described below in the Section 7, Future Work.4.

4.1 Mechanical Test Stands and Control Panels

Test Stations

Each cyclic test station (Fig. 9a) consists of a pair of pneumatic cylinders (TRD cylinders, 2.5”

bore, 3” stroke, bumper piston, over-sized rods; Cowper Inc., Kingston, ON, Canada), a prosthetic

foot-shank assembly, support brackets for the shank, a non-resetable mechanical stroke

counter (McMaster Carr, www.mcmaster.com) that records the number of test cycles completed,

and a magnetic limit switch (Model MRS-0.087-PXBL, 24 VDC reed switch, 2 wires with LED;

Cowper Inc., Kingston, ON, Canada) that detects excessive cylinder stroke length and, hence,

excessive deflection at the toe and heel. These components are mounted onto a 24”x30”x3/8”

aluminum plate (6061-T6), which is in turn screw mounted onto a test stand consisting of a

2”x4” frame secured onto a ¾” reinforced base. In total, there are two test stands housing

four testing stations (Fig. 9b).

Pneumatic and Electrical/Control Panels

Atop the test stands sit two 1”x6” boards onto which are secured the pneumatic and control

system components (Fig. 10a). The pneumatic components consist of 8 solenoid valves

(MAC series 55B; 24 VDC, 3/8” NPT ports, internal pilot, normally closed; Cowper Inc.) and 3

rapid control manifolds (Model RC303754; 0.5” inlet, 3/8” outlet, Cowper Inc.). The control

system is comprised of the main control box (Fig. 10b), DPDT relays (Daltco, Kingston, ON,

Canada), and a 24 VDC-2 Amp power supplies (Entrelec type, www.entrelec.com, Daltco,

Kingston, ON, Canada).

Electrical/Computer Panel

This panel (Fig. 11) is identical to the test station frames above, except that the aluminum

plate has been replaced by a ¾” plywood plate, onto which are mounted the 120 VAC supply

box, a 24 VDC-2.1 Amp power supply (IDEC switching type, A-Tech Instruments Ltd.,

Scarborough, ON, Canada), two signal conditioning modules (DSCA 41, DIN rail mount,

analogue, +/- 10 VDC out; purchased from A-Tech Instruments Ltd.), a back pressure regulator

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http://www.mcmaster.com/

http://www.entrelec.com/


(a) (b) Fig. 9. NPO Fatigue Tester Station. (a) Layout of components, including Niagara Foot [Series 3], shank and support brackets, 2 pneumatic cylinders, 2 magnetic limit switches, and a mechanical stroke counter. (b) Typical test frame, each of which houses 2 test stations.

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(a) (b)

Fig. 10. Pneumatics and Electrical/Control System (a) panel at top and bottom of figure, respectively. (b) the control box.

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Fig. 11. Electrical/Computer Panel. Mounted are a power supply box, a 24 VDC-2.1 Amp power supply, two signal conditioning modules, a back pressure regulator, and two proportional pressure controllers (PPCs).

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(Wilkerson Model R21-04-L00, 0.5” NPT; Cowper Inc., Kingston, ON, Canada), and two

proportional pressure controllers (PPCs) (MAC valve, 0-10 VDC control voltage, 0-100 psi;

Cowper Inc., Kingston, ON, Canada).

4.2 Pneumatics

The pneumatic network (Fig. 12) is powered by an air compressor (6.5 hp, 60 gal, vertical),

which acts as the main air supply for all test stations. The air pressure is regulated before

passing through an air filter (Wilkerson model VF18-04, Cowper Inc., Kingston, ON, Canada)

used to remove any moisture from the supply. The main supply line then branches from a

back pressure regulator and the two PPCs, one activating heel cylinders at all 4 stations and

the other the toe cylinders at all 4 stations. Thus, the cylinders apply load to the heel and toe.

The heel and toe PPCs each have their own manifold, which branch one air-flow inlet into 4

outlets. Each outlet is connected to a dedicated solenoid before being attached to the cylinder

inlet port. The solenoids are normally closed and must be powered to open and allow air to

flow into the cylinder inlet port.

In order to return the cylinders to an ‘off’ or ‘non-load’ position a small amount of back

pressure, controlled by the back pressure regulator, is required. Various combinations of

compressor pressure and back pressure, determined from a calibration table (Appendix 4),

can yield identical forces desired for a test.

The force and, hence, the speed at which the cylinders are retracted depend on the

application of a minimum back pressure level. The back pressure regulator is connected into

a manifold which has 1 inlet and 8 outlets that are connected into the exhaust ports of the

respective cylinders.

4.3 Electrical / Control System

Control Box

The operation of the entire fatigue tester is dictated by the control box (Figs. 10b and 13),

details for which are found in Appendix 5. The key switch controls power on/off, which

activates the green ‘Power On’ and ‘Ready’ lights. The red ‘Off’ switch is a momentary

contact switch that shuts down the control and pneumatics systems by cutting all electrical

power, causing solenoid valves to close and, hence, removing air supply to the cylinders.

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1

357

0

123

4

567

024

6

SOL1

SOL3

SOL7

SOL5

SOL0

SOL2

SOL6

SOL4

1 2

1 2

1 2

1 2

1 2

1 2

1 2

1 2

To Cylinder Exhaust 0To Cylinder Exhaust 1To Cylinder Exhaust 2To Cylinder Exhaust 3

To Cylinder Exhaust 4

To Cylinder Exhaust 5To Cylinder Exhaust 6


To Cylinder Inlet 0

To Cylinder Inlet 2

To Cylinder Inlet 4

To Cylinder Inlet 6

To Cylinder Inlet 1

To Cylinder Inlet 3

To Cylinder Inlet 5

To Cylinder Inlet 7

Heel Manifold

ToeManifold

ExhaustManifold

Regulator

Back PressureRegulator

Air Filter

Compressor(Main Supply)

ProportionalPressure

Controller


Controller

Solenoids

PNEUMATICS

PPC 0

PPC 1

1

357

1

357

0

123

4

567

0

123

0

123

4

567

4

567

024

6

024

6

SOL1

SOL3

SOL7

SOL5

SOL1

SOL3

SOL7

SOL5

SOL0

SOL2

SOL6

SOL4

SOL0

SOL2

SOL6

SOL4

1 2

1 2

1 2

1 2

1 2

1 2

1 2

1 2

To Cylinder Exhaust 0To Cylinder Exhaust 1To Cylinder Exhaust 2To Cylinder Exhaust 3


To Cylinder Exhaust 5To Cylinder Exhaust 6


To Cylinder Inlet 0

To Cylinder Inlet 2

To Cylinder Inlet 4

To Cylinder Inlet 6

To Cylinder Inlet 1

To Cylinder Inlet 3

To Cylinder Inlet 5

To Cylinder Inlet 7

Heel Manifold

ToeManifold

ExhaustManifold

Regulator

Back PressureRegulator

Air Filter

Compressor(Main Supply)


Controller


Controller

Solenoids

PNEUMATICS

PPC 0

PPC 1

Fig. 12. Schematic Layout for the Pneumatics system.

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Fig. 13. Schematic Layout for Electrical/Control box.

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5 6 7 8

1 2 3 4

SignalConditioner

0

5 6 7 8

1 2 3 4

SignalConditioner

1

xNC

xNC

NCx

- V+ V

24 VDC PowerSupply

N L

fromPPCs0 & 1

fromPPCs0 & 1

from PPC 1

Wires to Termination Board

from PPC 0

+ -

From 120 VPower Supply

1 – White +CMD2 – Red LMS23 – Green Common 6 Wires4 – Yellow LMS15 – Black Power 24 V6 – Blue -CMD

2 and 4 are Capped

PPC 0

1 – White +CMD2 – Red LMS23 – Green Common 6 Wires4 – Yellow LMS15 – Black Power 24 V6 – Blue -CMD

2 and 4 are Capped

PPC 1

ProportionalPressureControllers(PPCs)

x

ClearWhiteGreen

BlackRed

Analog Output - Green & WhiteGround - ClearAnalog Input - Black (in #1)

- Red (in #2)

TerminationPanel

ELECTRICAL / COMPUTER PANEL

Fig. 14. Schematic Layout for the Electrical/Computer system.

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Simultaneously, the red ‘Warning’ light is activated while the green ‘Ready’ light is turned

off, signifying there is an error or problem in the system. In order to reset the system, the

momentary contact ‘System Reset’ switch must be pressed, thus opening the solenoid valves.

The ‘Limit Over-ride’ toggle switch either sets or over-rides the magnetic limit switches,

described above. The control box is powered by one of two 24 VDC power supplies.

Relays

Each test station is equipped with a double-pole double-throw (DPDT) relay that controls the

switches and lights of the control box, as well as the solenoid valves and limit switches.

4.4 Electrical / Computer System

Signal Conditioners

Two signal conditioners (Fig. 14), one for each of the two PPCs, reduce signal noise levels

and remove potential disturbances caused by the 60 Hz frequency prior to the signal being

sent to the computer. The PPCs and signal conditioners are powered by a 24 VDC power

supply.

Computer System and Interface

All electrical connections to the computer occur via the termination panel (Model PCI-20429T,

Intelligent Instrumentation), which is plugged into the internal A/D data acquisition multi-

function board (Model PCI-20428W, Intelligent Instrumentation). The ‘Visual Designer’

software (Version 4 for Windows from Intelligent Instrumentation; purchased from A-Tech

Instruments Ltd., Scarborough, ON, Canada) creates sine waves used by the PPCs for cycling the

cylinders on and off in a sinusoidal wave pattern, and is used to collect and process raw data.

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5. OPERATING PROCEDURES FOR THE NPO FATIGUE TESTERTM The NPO fatigue tester experimental protocol can be described in terms of preparation of the

prosthesis for testing, test startup procedure, and test conditions.

5.1 Preparation of the Prosthesis for Testing Step 1. Foot Assembly (Fig. 15)

attach Otto Bock connector to foot

attach Otto Bock sleeve to shank

attach foot and shank

Step 2. Foot Alignment

all testing to be done on foot/shank with respect to ‘normal’ alignment:

o foot - 6° heel from horizontal (sagittal plane), no inversion/eversion

o shank - perpendicular to ground in frontal and sagittal planes

Step 3. Foot Mounting

remove nuts and washers from pylon connecting brackets

remove top piece of bracket and insert shank loosely

push cylinders to rest position (minimum stroke)

position foot such that acorn nut on top of heel cylinder (when cylinder is down) is approx. 10 mm from heel contact point; toe is about 1.5 inches from toe cylinder at this position

5.2 Test Startup Procedure Step 1. Initial Startup

open valve on air filter that is attached to air compressor

turn the compressor regulator on

plug in air compressor and power supply switch

turn on computer

Step 2. PPCs (Proportional Pressure Controllers)

set compressor regulator (which controls cylinder ‘on’ action) to desired pressure

set back stream pressure regulator (which controls cylinder ‘off’ action) to desired pressure

Note: pressures are different for each test depending on desired load (Appendix 4)

Step 3. Computer Control

execute ‘Visual Designer/Diagram’ and ‘Visual Designer/Run’ software programs which initiate sine wave form for actuator

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Fig. 15. Exploded view of the preparation of the Niagara [Series 3] foot-shank assembly for fatigue testing.

Time (s)

Load (N) Load Waveform for Fatigue Testing 970 N

50 N load ramp up

load ramp down

Fig. 16. Representative Load Waveform during Cycling Fatigue Testing.

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5.3 Test Conditions The following test conditions will be applied in the current study and, where cited, comply

directly with standards recommended by the International Organization for Standardization

(ISO, 1996), the full document being given in Appendix 1:

Temperature: approx. 23 °C or room temperature

Cycling Frequency: 1 Hz (since using plastic; ISO 2-6.4)

No. Cycles: 3 million cycles or until failure (ISO 4, Table 6)

Loads: cycle between 50-970 N (ISO 4, Table 6; ISO 3-4.4)

Cycling Waveform: sine wave (ISO 3-7.1, Fig. 3) as in Fig. 16

Niagara FootTM Size

o prosthesis rated for 60 kg person (A60 person; ISO 3-4.4), being the weight range of average amputee in the current target country (Cambodia)

o 24 cm length available (ISO 2-5.2)

Force-Foot Angles:

o heel-strike (15°) and toe-off (20°) (ISO 5-7.5, Fig 1; ISO 6-4, Table 7)

o angles cycled relative to ‘normal’ shank alignment described above

Failure Criteria for Cycling Testing:

o Test Completion: a test is considered complete when ‘failure’ occurs prior to reaching the prescribed 3 million cycles or when the 3 million cycles has been achieved with no failure of the test sample; ‘failure’ is defined and quantified in terms of deflection and force levels reached during (ISO 3-4.2, Table 6; ISO 3-7.3)

o Deflections: monitored by magnetic ‘reed’ limit switch, which is a band attached to the piston and a sensor placed on the cylinder surface; it is adjustable and shuts down solenoid valves at that station (ISO 3-5.4)

o Forces: axial forces on tibia/shank to be monitored with strain gages and not exceed critical values (ISO 4-4.2, Table 6)

- 22 -


6. A PILOT STUDY USING THE NPO FATIGUE TESTERTM This section summarizes briefly the results of preliminary fatigue tests performed on the

Niagara and SACH feet using the NPO Fatigue Tester.

6.1 Materials and Methods

Prosthetic Feet: Two variants of the Niagara Foot [Series 3] were tested. Niagara Foot A was

cut from a block of Delrin 150E using a water jet technique and was non-annealed. Niagara

Foot A* was also water jet cut from a block of the same material, but was also air annealed at

160°C (320°F) for 1.25 hours. Both feet were cut to the basic Niagara Foot shape and size

described earlier (Fig. 17a), being rated for a 60 kg individual and having a 24 cm length.

Full technical details of the U.S. patent for the foot can be found in Appendix 2. For

comparison, a Solid Ankle Cushion Heel (SACH) prosthetic foot (Fig. 17b) was also tested.

Test Protocol: The general test protocol and conditions were those described above in

Section 5, with the specific compressor and back stream pressures set at 80 and 25 psi,

respectively, to achieve a sinusoidal load range of 50-970 N for all runs. The SACH feet are

tested using a flat plate indenter, instead of the spherically ended indenters used for the

Niagara foot, to recreate desired load patterns because the SACH surface material is much

softer.

6.2 Results and Discussion

Results are summarized in Table 1. The tests reveal no catastrophic failure or signs of crack

initiation up to 63,000 cycles for the Niagara Foot. The current SACH foot is still undergoing

testing and has currently reached the 20,000 cycle mark, being too early to draw any

conclusions. However, as a point of comparison, the results of Wevers and Durance (1987)

on 4 different SACH feet betrayed cracks and early failure in the soles between 43,800 and

105,000 cycles. It is premature to perceive these results as an indication of the potential long-

term performance of the Niagara Foot relative to the SACH. Varying test conditions between

the studies may have played a role in the apparent differences: the current peak load levels

(50-970 N) were slightly below those of Wevers and Durance (1000-1350 N) for a given

loading cycle; the waveform of the present regime does not include a zero-load swing phase

but is rather continuous cycling of 50-970 N, unlike the SACH study which incorporates

- 23 -


swing; current test angles (heel-strike 15°, toe-off 20°) were slightly different from the

SACH study (heel-strike 17-20°, toe-off 57-61°). True comparison between prostheses

requires testing under exactly the same test conditions. Only further testing toward the 3

million loading cycles recommended by ISO and ISPO will reveal the actual mode(s) of

failure or wear of the Niagara and SACH feet, the extent of material softening, and the

effects of prosthesis construction and heat treatment method on performance.

(a) (b)

Fig. 17. Prosthetic Feet Tested (a) Niagara Foot [Series 3] (b) SACH Foot.

Table 1. Preliminary Test Results for Niagara and SACH Feet

Foot Type

Cycling Frequency

(Hz)

No. Cycles

Load Waveform

(N) Comments

Niagara Foot A 1 30,000 50-970 no signs of failure cracks; superficial

polishing tracks at toe and heel contact Niagara Foot A* 1 63,000 50-970 no signs of failure cracks; superficial

polishing tracks at toe and heel contact

SACH 1 20,000

(testing in progress)

50-970 at present, no signs of failure cracks or polishing tracks

- 24 -


7. INITIAL MATERIALS TEST RESULTS

7.1 Summary

There are two different types of testing that the ISO Standards require. One being the static

proof test or failure test and only once test samples have passed that test can they be cyclic

tested, which is the second type of testing required. (ISO 4-4.2)

After preliminary analysis at Queen’s University on the possible family of materials to use in

for the Niagara Foot, experts from Dupont were contacted and have been involved with the

final material selection procedures for the Niagara Foot.

7.2 Proof Testing

Protocol

The foot to be tested is inverted and mounted to a metal plate using the same mounting hole

as the connector for the completed assembly. The feet are held in place using a tool vice set

to the required angle for heel strike and toe off (15o and 200) respectively as stated in the ISO

Standards.

Fig. 18. Set up for Proof Testing: Exploded view (left) and assembled view (right) of Niagara

Foot and mounting plate

- 25 -


Fig. 19. Setup of the Instron for Proof Testing: Loads and deflections upon failure of the feet

at both heel strike (left) and toe-off (right) were determined

Testing was terminated when either the feet broke (catastrophic failure) or the deflection was

so great as to cause the heel to touch the back of the C-section or to cause the top of the toe to

touch the tool vice.

Prior to Dupont’s work on this project, failures were occurring with the feet at approximately

300 kg load. Dupont has since fine tuned the materials and suggested other variations of

Delrin® (Appendix 3) which have the necessary strength properties while allowing enough

deflection in the feet to cause a termination of testing rather than catastrophic failures.

Results for the last 15 Delrin® injection molded feet are included in Appendix 7.

7.3 Cyclic Fatigue Testing

Once feet have passed the proof testing, they go onto cyclic fatigue testing. Feet are

currently tested to ISO Standards however in the future, the ISO tests may be modified to

allow for a better representation of the actual biomechanical forces generated throughout a

gait cycle.

At the present time, spot inspections on the cyclic testers are performed every half hour and

complete inspections are performed every four hours. Details of these inspections can be

found in Appendix 8.

- 26 -


After the first 100,000 cycles on the tester, Zytel® ST801 (Nylon) was discarded as a

potential candidate as it appeared that permanent plastic deformation occurred. Failure

occurred on the SACH foot during this time (the first 100,000 cycles) as well. All of the

Delrin® versions of the feet that have been tested to date have made it past this crucial point.

(Appendix 9)

Photos are taken daily of the feet being tested and compared to a profile of the feet as well as

compared to previous days photos. Reports are generated on a regular basis, several of

which are found in Appendix 10.

- 27 -


8. FUTURE WORK

8.1 Validation and Calibration of the NPO Fatigue Tester

Calibration of Axial Force Measurements

To ensure that the fatigue tester axial force measurements are accurate and repeatable, the

tibial shank used for cycling testing will be instrumented with strain gages arranged in the

Wheat Stone bridge configuration used during actual test runs (Fig. 18). The shank will be

placed in an Instron machine (model 1122), known axial compressive forces will be applied,

and the corresponding strain gage voltages recorded. This calibration is required annually

and must be accurate within +/- 1% (ISO 3-9).

Calibration of Cycling Frequency

To ensure that the cycling frequency of choice is maintained during testing to within +/- 10%

(ISO 3-9), annual calibration will be done using a mechanical stroke counter (model A,

McMaster-Carr, Dayton, NJ, www.mcmaster.com) and stop watch for several trials of 1

minute duration.

Comparison with Gait Analysis

To ensure that the NPO Fatigue Tester mimics adequately the axial tibial force levels and

waveforms experienced by the prosthesis in the field, measurements of axial forces will be

measured during cycling testing of the Niagara Foot and compared to data from two separate

gait studies, described below, one for normals and the other for below knee amputee subjects.

1. Fatigue Tester Force Measurements (to be done)

Test Procedure - using Wheat Stone bridge strain gage circuit, axial forces acting along the tibial shank of the prosthesis during cyclic fatigue testing of the Niagara Foot will be measured

Test Conditions - as described in Section 5.3 above

2. Gait Tests for Normals (completed)

Test Procedure - IRED (infra-red emitting diode) markers placed on lateral aspect of their test leg at bony landmarks; Watsmart (Northern Digital, ON) video system used to record motion / kinematic data; embedded force plate in raised walkway recorded force / kinetic data; motion and force data sampled at 50 Hz

Test Conditions - n = 34 subjects, average age (24.5 yrs), average weight (65.4 kg), average height (171 cm), level walking frequency = naturally chosen by subject

- 28 -

http://www.mcmaster.com/


1

24

3

XY

Z

Note: 350 Ω Strain Gages

Shank

StrainGage

ForceFX

MomentMY

MomentMX

1 + + 02 - 0 -3 - 0 +4 + - 0

Fig. 18. Strain gage arrangement on the tibial shank for measuring axial tibial force (FX) and moments (MX and MY).

- 29 -


3. Gait Tests for Below Knee Amputees (to be done)

Test Procedure - the tibial shank will be instrumented with a Wheat Stone bridge strain gage circuit to measure tibial axial forces

Test Conditions - gait study performed on adult below knee amputees in level walking, Niagara Foot prosthesis used, number of subjects and trials per subject yet to be determined

8.2 Waveform Modifications

In the field, it is expected that the prosthesis will be subject to load levels typical of non-gait

conditions and events (e.g. kicking, climbing, rough terrain). In addition, the mechanical

durability of the Niagara Foot may be ‘successful’ in that it exceeds the 3 million cycles

recommended by ISO standards. Thus, one of the methods used to simulate non-gait events

and assess the failure mode of ‘successful’ prostheses, is to modify the load waveform (Fig.

16) either by gradually increasing peak-to-peak loading or the load baseline level imposed on

the foot until failure eventually occurs. Although, this does not accurately predict the fatigue

strength of the foot, it allows manufacturers to make inter-prosthesis comparisons by

observing how and at what load levels failures occur.

8.3 Environmental Durability of the Niagara Foot

Environmental Conditions

Because of the various environments the foot will potentially be exposed to, the danger of

severe material degradation of the Niagara Foot exists. To this end, the resistance of the foot

material to anticipated conditions such as thermal and UV sunlight exposure, humidity,

saltwater, micro-organisms and mechanical abrasion, should be tested. During previous

clinical studies (Potter 2000; Potter et al., 1999), a layer of polyurethane rubber was attached

to the sole of the Niagara 1 version of the Niagara Foot to provide some cushioning for the

client and for protection of the Hivalloy G7062 (20% glass-filled polypropylene) material

from abrasion. In order to assess the effect of more adverse conditions during gait, the bond

between the rubber sole and the foot should also be examined. To these ends, a series of

standard tests are available from the American Society for Testing and Materials (ASTM):

aerobic biodegradability of degradable plastics by micro-organisms (ASTM D5247) outdoor accelerated weathering of plastics using concentrated sunlight (ASTM

D4364)

- 30 -


response of rigid cellular plastics to thermal and humid aging (ASTM D2126) weathering of plastics under marine floating exposure (ASTM D5437) resistance of plastics to abrasion (ASTM D1242) peel or stripping strength of adhesive bonds (ASTM D903)

Related Materials Issues

The importance of examining material microstructure of the material before and after

mechanical fatigue and environmental resistance tests has been suggested. The detection of

structural change and weakness may be especially significant in areas where high stresses are

expected. One available method developed by our group (Dwyer, 1996) detects localized

regions of structural weakness by the level of oxidation present using an SO2 staining

technique. Finally, in order to minimize waste, further reduce foot cost, and catalyze

technology transfer to the host community, the possibility of using local waste plastics for re-

processing can be investigated (Bunton et al., 1999).

8.4 Complete Sized Modular System

The next project will be to design residual limb sockets in a range of sizes to fit an initial

target population. The majority of amputees are affected in the lower limb, below the knee

(BK). The most common approach to provide prostheses for these patients is to use a

modular system composed of a foot, pylon and socket. Feet are generally available in a

series of sizes and styles, while sockets require custom fitting to ensure proper load transfer

to the residual limb. All components are expensive by world standards, since the majority of

amputees are in developing countries. It is proposed that the use of modern design and

fabrication methods could greatly reduce these costs, increasing accessibility. Previous work

has produced a low cost foot component fabricated by injection molding; the specific

objective of this project is to design and test a sized modular socket system produced using

mass production methods.

The socket project has five phases as described below: socket sizing using statistical

methods, internal shape and size optimization to ensure fit, stress analysis and material

selection, initial prototype fabrication, and durability testing. The components will be

manufactured in Ontario for a global market of amputees that are currently under serviced by

expensive custom-made devices.

- 31 -


1. Collection of Anthropometric Data (NPO) Development of sampling method Statistical analysis of data set

2. Sizing Using CAD Interference Method (Queen’s University) Importing of data and data reduction in CAD program Determination of characteristics of fit Determination of suitable size range for sample population

3. Stress Analysis of Socket-Pylon Interface (Queen’s University) Simulation of loading at socket-pylon interface Material characterization

4. Prototyping (NPO) Creation of forms for various sizes for the chosen manufacturing method Verification of fit using blown liners

5. Mechanical Testing (Queen’s University) Modification of tester to accept residual limb form Verification of instrumentation Determination of tibial forces using gait analysis Test of initial set of sockets

8.5 Cosmetic Cover for Foot

In some cultures, the appearance of a prosthetic device is of almost equal importance as its

functionality. To this end, Boyer (2001) developed a cosmetic cover for the Niagara Foot,

which has a strictly cosmetic purpose and is not necessary for the proper function of the

prosthesis. The cover is a leather boot based on a positive mold of a natural foot the same

length as that of the prosthesis. The design is unisex, ambidextrous, simple, and low in cost.

The proposed manufacturing scheme involves local shoemakers, thereby minimizing

specialized training, and local materials, thereby minimizing cost. Distribution of a cosmetic

cover pattern with each prosthesis to local shoemakers is envisioned. A prototype cover has

been constructed and is available for focus group evaluation, from which modifications can

be made. The full report by Boyer (2001) is available upon request.

8.6 Modification of Test Stands

The current tester is a first working model made to ensure that all components functioned as

expected. As such, the stands for the stations and control panels are temporary. New stands

and panels will be constructed that are ergonomic, functional, and versatile (Appendix 6).

The proposed design concept is the result of an unpublished study (Fisher et al., 2001).

- 32 -


9. FINAL REMARKS

In many post-conflict and developing countries, prostheses are used on rough physical

terrain. The current mechanical fatigue tester uses a standardized cyclic loading regime that

mimics normal walking conditions and potential damage events (kicking, tripping,

negotiating rough terrain, etc.) Testing will be consistent with the voluntary international

standards developed by ISO (1996) and ISPO (1978), which have been used by few

researchers (Daher, 1975; Toh et al., 1993), two of which were undertaken by our research

group (Singleton, 1983; Wevers and Durance, 1987). The success of the NPO Fatigue Tester

could make Canada an international centre for durability testing of prosthetic lower limbs

and feet. Also, because the SACH prosthesis is commonly used in developing countries,

benchmark tests will be done for comparison with the Niagara Foot. Finally, since

preliminary tests show that the Niagara Foot’s durability and performance exceeds that of the

SACH, the Niagara Foot's cost - 10% of a low end $ 75 (U.S.) SACH - and manufacturing

ease, would make it the foot of choice.

- 33 -


REFERENCES Barth DG, Schumacher L, Thomas SS. “Gait Analysis and Energy Cost of Below-Knee Amputees Wearing Six Different Prosthetic Feet.” J. Prosthetics and Orthotics, 4(2):63-75, 1991.

Boyer K. A Cosmetic Cover for the Niagara Prosthetic Foot. MECH 461 Course Report, Mechanical Engineering Dept., Queen’s University, Kingston, ON, Canada, April 2001. Bunton, E, Kenney, S, Meilenner, C, and S Wilson, Low Cost Wheels, MECH 212 Design Project, Mechanical Engineering Dept., Queen’s University, Kingston, ON, Canada, 1999. Carlson JM, Day B, Berglund G. “Double Short Flexure Type Orthotic Ankle Joints.” J. Prosthetics and Orthotics, 2(4):289-300, 1990.

Daher RL, “Physical Response of SACH Feet under Laboratory Testing”, Bulletin of Prosthetics Research, 10(23):4-50, 1975. Dwyer, KA, Effect of Heterogeneous Structure on Ultra High Molecular Weight Polyethylene Failure Mechanisms in Total Joint Arthroplasty, PhD Thesis, Mechanical Engineering Dept., Queen’s University, Kingston, ON, Canada, 1996. Fisher J, Burnier E, Johansen C, Corley J. Test Stand for Fatigue Tester. MECH 212 Course Report, Mechanical Engineering Dept., Queen’s University, Kingston, ON, Canada, April 2001. ISO (International Organization for Standardization), Prosthetics – Structural Testing of Lower-Limb Prostheses, Reference No. ISO 10328:1-8 / 1996E, 1996.

ISPO (International Society for Prosthetics and Orthotics), Standards for Lower-Limb Prostheses – Report of a Conference 1977, 1978.

Macfarlane PA, Nielsen DH, Shurr DG, Meier K. “Gait Comparisons for Below-Knee Amputees using a Flex-Foot versus a Conventional Prosthetic Foot.” J. Prosthetics and Orthotics, 3(4):150-161, 1990.

Menard MR, Murray DD. “Subjective and Objective Analysis of an Energy-Storing Prosthetic Foot”. J. Prosthetic and Orthotics, 1(4):220-230, 1989.

Noce-Kirkwood R. Kinematic and kinetic analysis of the hip joint during level walking, stair climbing and exercise protocols, PhD Thesis, School of Physical and Health Education, Queen’s University, Kingston, ON, Canada, 1997.

Pitkin MR. “Mechanical Outcomes of a Rolling-Joint Prosthetic Foot and Its Performance in the Dorsiflexion Phase of Transtibial Amputee Gait.” J. Prosthetics and Orthotics, 7(4):114-123, 1995.

Potter DW. Gait Analysis of a New Low Cost Foot Prosthetic for use in Developing Countries. M.Sc Thesis, School of Physical and Health Education, Queen’s University, Kingston, ON, Canada, 2000.

Potter D, Costigan P, Bryant JT, and R Gabourie, "Clinical Gait Trial of a New Prosthetic Foot Design for Developing Countries", International Society of Biomechanics, 17th Congress, Calgary, Canada, Aug. 8-13, 1999.

Singleton JD, A Fatigue Tester for Below-Knee Prostheses, M.Sc. Thesis, Mechanical Engineering Dept., Queen’s University, Kingston, ON, Canada, 1983.

Toh SL, Goh JCH, Tan PH, and TE Tay, “Fatigue Testing of Energy Storing Prosthetic Feet”, Prosthetics and Orthotics International, 17:180-188, 1993.

Tsai A, “A Summary of the Initial Phase of the NPO Low Cost Modular Prosthetic Foot Project”, Technical Report, Clinical Mechanics Group (Kingston General Hospital), Queen’s University, Kingston, ON, Canada, Apr. 25, 1999.

Valenti TG. “Experience with Endoflex: A Monolithic Thermoplastic Prosthesis for Below Knee Amputees.” J. Prosthetics and Orthotics, 3(1):43-50, 1990.

Wevers HW and JP Durance, “Dynamic Testing of Below-Knee Prosthesis: Assembly and Components”, Prosthetics and Orthotics International, 11:117-123, 1987.

- 34 -


Wong P, Addison G, Austin M. Control System for Prosthetic Foot Cyclical Testing Machine. MECH 212 Course Report, Mechanical Engineering Dept., Queen’s University, Kingston, ON, Canada, April 2001.

Yamamoto S, Ebina M, Kubo S, et al. “Quantification of the Effect of Dorsi-Plantarflexibility of Ankle-Foot Orthoses on Hemiplegic Gait: A Preliminary Report.” J. Prosthetics and Orthotics, 5(3):88-94, 1992.

Ziolo T, Stress Analysis and Design Optimization of an Injection Molded Prosthetic Foot, Undergraduate Thesis, Mechanical Engineering Dept., Queen’s University, Kingston, ON, Canada, 1999.

- 35 -


APPENDIX 1 – ISO TESTING STANDARDS

FOR PROSTHESES


APPENDIX 2 – U.S. PATENT FILE

FOR THE NIAGARA FOOT


APPENDIX 3 – MATERIAL PROPERTIES


APPENDIX 4 – PPC Calibration Tables


Inlet Pressurepsi 0 psi 5 psi 10 psi 15 psi 20 psi 25 psi 30 psi 35 psi 40 psi

5 109 17 -74 -166 -258 -349 -441 -533 -610 218 127 35 -57 -148 -240 -332 -424 -515 328 236 144 52 -39 -131 -223 -314 -40620 437 345 253 162 70 -22 -114 -205 -29725 546 454 362 271 179 87 -4 -96 -18830 655 563 472 380 288 197 105 13 -7935 764 673 581 489 397 306 214 122 3140 873 782 690 598 507 415 323 231 14045 983 891 799 707 616 524 432 341 24950 1092 1000 908 817 725 633 542 450 35855 1201 1109 1018 926 834 742 651 559 46760 1310 1218 1127 1035 943 852 760 668 57665 1419 1328 1236 1144 1052 961 869 777 68670 1528 1437 1345 1253 1162 1070 978 887 79575 1638 1546 1454 1363 1271 1179 1087 996 90480 1747 1655 1563 1472 1380 1288 1197 1105 101385 1856 1764 1673 1581 1489 1397 1306 1214 112290 1965 1873 1782 1690 1598 1507 1415 1323 123295 2074 1983 1891 1799 1708 1616 1524 1432 1341

100 2184 2092 2000 1908 1817 1725 1633 1542 1450105 2293 2201 2109 2018 1926 1834 1742 1651 1559110 2402 2310 2218 2127 2035 1943 1852 1760 1668115 2511 2419 2328 2236 2144 2053 1961 1869 1777120 2620 2529 2437 2345 2253 2162 2070 1978 1887

The Net Force Exerted on Foot (N) Using 2.5" Bore Cylinders (CYCLIC TESTING)

Back Pressure

2415

Inlet Pressurepsi 0 psi 5 psi 10 psi 15 psi 20 psi 25 psi 30 psi 35 psi 40 psi

5 185 33 -118 -270 -421 -573 -724 -876 -102710 369 218 66 -85 -237 -388 -540 -691 -84315 554 402 251 99 -52 -204 -355 -507 -65820 738 587 435 284 132 -19 -171 -322 -47425 923 771 620 468 317 165 14 -138 -28930 1107 956 804 653 501 350 198 47 -10535 1292 1140 989 837 686 534 383 231 8040 1476 1325 1173 1022 870 719 567 416 26445 1661 1509 1358 1206 1055 903 752 600 44950 1845 1694 1542 1391 1239 1088 936 785 63355 2030 1878 1727 1575 1424 1272 1121 969 81860 2214 2063 1911 1760 1608 1457 1305 1154 100265 2399 2247 2096 1944 1793 1641 1490 1338 118770 2583 2432 2280 2129 1977 1826 1674 1523 137175 2768 2616 2465 2313 2162 2010 1859 1707 155680 2952 2801 2649 2498 2346 2195 2043 1892 174085 3137 2985 2834 2682 2531 2379 2228 2076 192590 3321 3170 3018 2867 2715 2564 2412 2261 210995 3506 3354 3203 3051 2900 2748 2597 2445 2294

100 3690 3539 3387 3236 3084 2933 2781 2630 2478105 3875 3723 3572 3420 3269 3117 2966 2814 2663110 4059 3908 3756 3605 3453 3302 3150 2999 2847115 4244 4092 3941 3789 3638 3486 3335 3183 3032120 4428 4277 4125 3974 3822 3671 3519 3368 3216

Back Pressure

Net Force Exerted on Foot (N) Using 3.25" Bore Cylinders (PROOF TESTING)

APPENDIX 5 – CONTROL SYSTEM

(TECHNICAL REPORT)

1

APPENDIX 6 – TEST STAND

MODIFICATIONS

(NOTE: not included in soft copy)

APPENDIX 7 – RESULTS OF

PROOF TESTING

APPENDIX 8 – INSPECTION SHEETS FOR CYCLIC TESTING

APPENDIX 9 – CYCLIC FATIGUE TESTING REPORT

APPENDIX 10 – DEFORMATION OF

FEET DURING CYCLIC TESTING

Documents

THE NPO FATIGUE TESTER - Niagara Foot Tester.pdf · The NPO Fatigue Tester Ziolo, Zdero, and Bryant (2001) 2. WORK TO DATE SUMMARY The Niagara FootTM was designed by the Human Mobility